Background: Epidural morphine for postoperative pain control has a serious risk of respiratory depression and other side effects such as pruritus, nausea and urinary retention. In recent years, it is known that epidural administration of ketamine potentiates the effect of epidural morphine, and so decrease the side effects of epidural morphine. This study was performed to evaluate the analgesic efficacy of epidurally administered ketamine and whether this epidural administration can decrease the amount of epidural morphine. Methods: Sixty patients scheduled for the elective cesarean section were randomly selected. All patients were given subarachnoid injection of tetracaine 9 mg. Group I received epidural bolus injection of 0.15% bupivacaine 10 ml with morphine 2 mg followed by a continuous infusion of 0.125% bupivacaine 100 ml containing morphine 4 mg after peritoneum closure, and group II received the same method as group I except for the addition of epidural ketamine 30 mg. Analgesic effects were assessed using Numeric Rating Score (NRS) and Prince Henry Score (PHS). Also, the degree of satisfaction and the incidence of the side effects were observed. Results: Analgesic effects were significant in both groups after drug administration. But NRS and PHS were not significantly different between two groups at all times. The incidence of nausea and vomiting was 11 out of 30 in group I and 9 out of 30 in group II and the incidence of itching was 11 out of 30 in group I and 8 out of 30 in group II. Number of patients using additional analgesics were 2 and 1 in group I and II, respectively. Conclusions: Epidural ketamine did not potentiate the analgesic effect of epidural morphine and could not decrease the side effect of epidural morphine.